1. Field of the Invention
This invention relates to trusses and particularly to a new and improved truss which is deployable for supporting components, such as solar panels, and yet which can be compactly folded.
2. Description of the Prior Art
Trusses employed for certain uses are required to be variable in size. For example, a large space structure, such as that which supports an orbiting solar panel array, must be able to fit into a limited capacity launch vehicle during its launch into space. Yet once in space, the structure must be capable of expanding to a relatively large size in order to support a large solar array.
Different types of deployable trusses, that is, trusses which can expand from folded to unfolded, or deployed, configurations, as well as varying arrangements for folding the truss members, have been developed. In some cases, the structural integrity of the truss, rather than compactness, has been emphasized, resulting in large, heavy truss members. The overall size of such a truss once it deploys is therefore kept relatively small due to size and weight limitations of the launch vehicle. Correspondingly, the size of the solar array supported by the truss is also relatively small making it difficult to justify the high cost of launching the truss into space.
On the other hand, efforts at minimizing the folded size of deployable trusses in order to meet the launch vehicle size limitation while maintaining the large deployed size of the trusses have sometimes resulted in structural deficiencies when the trusses are deployed. Deficiencies in three structural areas are of concern: bending stiffness, torsional stiffness and thermal stability. Ideally, each should be maximized when the truss is deployed in order to provide a stable, long-life platform for solar panels or other components supported by the truss. One means of maximizing bending stiffness and torsional stiffness is by increasing the size of the truss relative to the size of the solar panels it supports. For example, increasing the height of a truss in a direction normal to the surface of the solar panel it supports would correspondingly increase the bending stiffness and torsional stiffness of the truss-panel structure. Also, a taller truss improves the thermal stability of the truss, that is, the resistance of the truss to deflection caused by differences in temperature between different members of the truss. The greater the distance between two parallel members of the truss which are subject to differing temperatures, the less will be the deflection caused by the temperature differential. Yet modifying current deployable truss designs by increasing the height of the truss would result in the folded truss being larger than originally designed and therefore perhaps too large to fit in a launch vehicle.
In view of the above mentioned problems, it is therefore an object of the present invention to provide a deployable truss which is relatively large when deployed yet which can be compactly folded.
Another object of the present invention is to provide a deployable truss having increased bending stiffness and increased torsional stiffness for better supporting an array of panels.
Yet another object of the present invention is to provide a deployable truss with increased thermal stability.